Myocardial blood volume (MBV) is the volume of blood in the coronary microcirculation. Changes in myocardial blood flow (MBF) during normal physiologic conditions and during disease states are modulated via changes in MBV. The noninvasive assessment of MBV, therefore, has the potential of providing unique insights into coronary pathophysiology during health and disease. An assessment of MBV, however, requires that the perfusion tracer be located entirely within the intravascular space during its transit through the coronary microcirculation. Small microbubbles of air, of the size of red blood cells, have been shown to have this property. Their transit through the myocardium can be imaged using two-dimensional echocardiography. This research proposal aims to use this technique to measure MBV in 3 different canine models which will be created to address 3 specific hypotheses relating to the value of measuring MBV in ischemic heart disease.